In general, known in the art as a method of removing a soluble component, such as salt, from polymer powder or oxidized powder, are a sedimentation method that precipitates soluble component-containing powder mixed with a solvent in a tank, thereafter repeats separating of the precipitated powder from the solvent containing the dissolved soluble component and a centrifugal method that separates particles by rotating a container filled with a solution where soluble component-containing powder and a solvent are mixed, using a difference in density of the solution and powder.
A known sedimentation method, however, is rapidly processed when the particles of soluble component-containing powder is 10 μm or more in size, whereas when the particles are smaller than that and have floatability, it takes a long time to precipitate the powder, which results in extending the process cycle to separate the powder from the solution and deteriorating workability.
On the other hand, as for washing by a centrifugal method, when a large amount of particles are contained, a motor rotating a container at high speeds may overload and break down.
Further, an example for overcoming the problems in the art is disclosed in Japanese Patent Application Publication No. 2004-358288, titled “METHOD FOR WASHING/DESALTING INCINERATION ASH”. According to the method, soot and dust produced when combustible waste is incinerated are incorporated with inorganic powder of 10 to 200 μm in average particle size, and a mixture is incorporated with water to make slurry. The slurry is separated into inorganic solids and an aqueous solution in which salts are dissolved by a solid-liquid separation process using a belt filter.
The aforementioned method, however, has a problem in that even though the washing/desalting is effectively processed by loading of a filter, solids of which particle size is about 1 μm due to the limitation of unwoven fabric may come out and not only a large amount of space and cost for mounting the belt filter are required, but a specific process is required to separate the inorganic solids from the surface of the filter.